Heat treatment method and heat treatment apparatus for heating substrate by light irradiation

ABSTRACT

A semiconductor wafer in which a carbon thin film is formed on a surface of a silicon substrate implanted with impurities is irradiated with flash light emitted from flash lamps. Absorbing the flash light causes the temperature of the carbon thin film to increase. The surface temperature of the silicon substrate implanted with impurities is therefore increased to be higher than that in a case where no thin film is formed, and the sheet resistance value can be thereby decreased. When the semiconductor wafer with the carbon thin film formed thereon is irradiated with flash light in high concentration oxygen atmosphere, since the carbon of the thin film is oxidized to be vaporized, removal of the thin film is performed concurrently with flash heating.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.12/732,591, filed Mar. 26, 2010, by Shinichi KATO, entitled HEATTREATMENT METHOD AND HEAT TREATMENT APPARATUS FOR HEATING SUBSTRATE BYLIGHT IRRADIATION which claims the benefit of Japanese Appln. S.N.JP2009-109318, filed Apr. 28, 2009 and Japanese Appln. No.JP2010-018128, filed Jan. 29, 2010, the contents of which areincorporated by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat treatment method and a heattreatment apparatus both of which are used for heating a thin plate-likeprecision electronic substrate such as a semiconductor wafer, a glasssubstrate for a liquid crystal display device, a glass substrate for aphotomask and a substrate for an optical disk (hereinafter referred tosimply as a “substrate”), which is implanted with impurities, byirradiating the substrate with flash light.

2. Description of the Background Art

Conventionally, a lamp annealer employing halogen lamps has beencommonly used in the step of activating impurities in a semiconductorwafer after impurity implantation. Such a lamp annealer carries out theactivation of impurities in a semiconductor wafer by heating (orannealing) the semiconductor wafer up to a temperature of, e.x., about1000° C. to 1100° C. In such a heat treatment apparatus, the energy oflight emitted from halogen lamps is used to raise the temperature of asubstrate at a rate of about several hundred degrees per second.

Meanwhile, in recent years, with increasing degree of integration ofsemiconductor devices, it has been desired that the junction should bemade shallower as the gate length is shortened. It has turned out,however, that even if the above lamp annealer, which raises thetemperature of a semiconductor wafer at a rate of about several hundreddegrees per second, is used to carry out the activation of impurities ina semiconductor wafer, there still occurs a phenomenon that impuritiessuch as boron or phosphorous implanted in the semiconductor wafer aredeeply diffused by heat. There is apprehension that the occurrence ofsuch a phenomenon may cause the depth of the junction to exceed therequired level, thereby hindering good device formation.

To solve the problem, U.S. Pat. No. 6,998,580 and U.S. Pat. No.6,936,797 propose techniques for raising only the surface temperature ofa semiconductor wafer implanted with impurities in an extremely shortperiod of time (several milliseconds or less) by irradiating the surfaceof the semiconductor wafer with flashes of light from xenon flash lamps(the term “flash lamp” as used hereinafter refers to a “xenon flashlamp”). The xenon flash lamps have a spectral distribution of radiationranging from ultraviolet to near-infrared regions. The wavelength of thelight emitted from the xenon flash lamp is shorter than that of thelight emitted from the conventional halogen lamp, and it almostcoincides with the fundamental absorption band of a siliconsemiconductor wafer. Therefore, when a semiconductor wafer is irradiatedwith the flashes of light emitted from the xenon flash lamps, thetemperature of the semiconductor wafer can be raised quickly with only asmall amount of light transmitted through the semiconductor wafer. Ithas also turned out that the flashes of light emitted within anextremely short period of time such as several milliseconds or lessallow a selective temperature rise only near the surface of asemiconductor wafer. For this reason, such a temperature rise caused byusing the xenon flash lamps in an extremely short time allows only theactivation of impurities to be implemented without deep diffusion of theimpurities.

Now, as a typical measure of the properties of semiconductor wafersimplanted with impurities, used is a sheet resistance value Rs. Sincethe activation of impurities decreases a sheet resistance value on thesurface of a semiconductor wafer, a lower sheet resistance valuegenerally indicates that better activation of impurities is achieved.For this reason, a further decrease in the sheet resistance value isdesired. In order to decrease the sheet resistance value, the surfacetemperature of a semiconductor wafer has only to be further increased.

In order to further increase the attained surface temperature of asemiconductor wafer to be still higher with the emission of flashes oflight from flash lamps, however, it is necessary to emit flashes oflight with greater irradiation energy in an extremely short period oftime, which must result in an increase in the loads of both flash lampsand driving circuits therefor. Consequently, there also arises a problemof shortening the lifetimes of such flash lamps.

Further, since the intensity distribution of flash light in the surfaceof a semiconductor wafer is not completely uniform and fine patterns areformed on the surface of the semiconductor wafer, the inplanedistribution of light absorptivity is not also uniform. Consequently,there is also variation in the inplane temperature distribution of thesemiconductor wafer when the semiconductor wafer is irradiated withflashes of light.

A tendency is found that the intensity becomes higher in the peripheralportion of a semiconductor wafer than that in the central portionthereof also due to the effect of reflection on a chamber wall surfaceor the like. Consequently, there is also variation in the inplanetemperature distribution of the semiconductor wafer when thesemiconductor wafer is irradiated with flashes of light, with a tendencythat the temperature is more apt to increase in the peripheral portionthan in the central portion. Moreover, it is very difficult to cancelthe variation in the inplane temperature distribution in a heattreatment with irradiation using flash light in an extremely shortirradiation time.

SUMMARY OF THE INVENTION

The present invention is intended for a heat treatment method forheating a substrate implanted with impurities by irradiating thesubstrate with flash light.

According to an aspect of the present invention, the heat treatmentmethod comprises the steps of forming a carbon or carbon compound thinfilm on a surface of a substrate implanted with impurities, housing asubstrate with a thin film formed thereon in a chamber, and irradiatingthe substrate housed in the chamber with flash light emitted from aflash lamp.

Since the carbon or carbon compound thin film is formed on the surfaceof the substrate implanted with impurities and the substrate isirradiated with flash light emitted from the flash lamp, the thin filmabsorbs the flash light to raise the temperature thereof and it isthereby possible to increase the surface temperature of the substrate tobe still higher and decrease the sheet resistance value.

Preferably, the heat treatment method further comprises the step ofintroducing oxygen gas into the chamber after housing the substrate inthe chamber and before emitting flash light.

Since oxygen gas is supplied into the chamber before emitting flashlight, the thin film is oxidized during the irradiation with flash lightto allow removal of the thin film to proceed and the nonuniformy in thetemperature distribution due to the variation in the intensity of flashlight can be cancelled.

According another aspect of the present invention, the heat treatmentmethod comprises a thin film formation step of forming a thin filmhaving a nonuniform film thickness distribution on a surface of asubstrate implanted with impurities, and a light emission step ofemitting flash light from a flash lamp to the substrate with the thinfilm formed thereon.

With the thin film having a nonuniform film thickness distribution, thevariation in the intensity distribution of flash light can be cancelledand the surface temperature of the substrate can be raised uniformly.

Preferably, a thin film is formed on a surface of the substrate so thatthe film thickness thereof becomes smaller from the central portion ofthe substrate toward the peripheral portion thereof in the thin filmformation step.

The variation in the intensity distribution of flash light in which thelight intensity becomes higher in the peripheral portion than in thecentral portion can be cancelled, and the surface temperature of thesubstrate can be thereby raised uniformly.

The present invention is intended for a heat treatment apparatus forheating a substrate implanted with impurities by irradiating thesubstrate with flash light.

According to an aspect of the present invention, the heat treatmentapparatus comprises a chamber for housing a substrate in which a carbonor carbon compound thin film is formed on a surface thereof after beingimplanted with impurities, a holding part for holding the substrate inthe chamber, and a flash lamp for emitting flash light to the substrateheld by the holding part.

Since the substrate with the carbon or carbon compound thin film formedthereon after impurities are implanted therein is irradiated with flashlight emitted from the flash lamp, the thin film absorbs the flash lightto raise the temperature thereof, and it is thereby possible to increasethe surface temperature of the substrate to be still higher and decreasethe sheet resistance value.

Preferably, the heat treatment apparatus further comprises an oxygenintroduction part for introducing oxygen gas into the chamber.

Since oxygen gas is introduced into the chamber, the thin film isoxidized during the irradiation with flash light to allow removal of thethin film to proceed and the nonuniformy in the temperature distributiondue to the variation in the intensity of flash light can be cancelled.

According to another aspect of the present invention, the heat treatmentapparatus comprises a chamber for housing a substrate in which a carbonor carbon compound thin film is formed on a surface thereof after beingimplanted with impurities, a holding part for holding the substrate inthe chamber, a preheating part for preheating the substrate held by theholding part, a flash lamp for emitting flash light to the substrateheld by the holding part, an oxygen gas supply part for supplying oxygengas from around the substrate held by the holding part in the chamber,an exhaust part for exhausting the atmosphere in the chamber from belowthe substrate held by the holding part, and a control part configured tocontrol the preheating part to heat the substrate held by the holdingpart, control the oxygen gas supply part to supply oxygen gas whilecontrolling the exhaust part to exhaust the atmosphere from the chamber,to thereby make the film thickness smaller from the central portion ofthe thin film formed on the surface of the substrate toward theperipheral portion thereof, and then control the flash lamp to emitflash light.

With the thin film of which the film thickness becomes smaller from itscentral portion toward its peripheral portion, the variation in theintensity distribution of flash light in which the light intensitybecomes higher in the peripheral portion than in the central portion canbe cancelled and the surface temperature of the substrate can be raiseduniformly.

Therefore, it is an object of the present invention to increase thesurface temperature of the substrate and decrease the sheet resistancevalue.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section showing a configuration of a heattreatment apparatus in accordance with a first preferred embodiment ofthe present invention.

FIG. 2 is a cross section showing a gas passage of the heat treatmentapparatus of FIG. 1.

FIG. 3 is a cross section showing a structure of a holder.

FIG. 4 is a plan view showing a hot plate.

FIG. 5 is another longitudinal section showing the configuration of theheat treatment apparatus of FIG. 1.

FIG. 6 is a block diagram showing a constitution of a controller inaccordance with the first preferred embodiment.

FIG. 7 is a flowchart showing part of an operation flow of processing asemiconductor wafer in accordance with the first preferred embodiment.

FIG. 8 is a flowchart showing process steps for processing thesemiconductor wafer in the heat treatment apparatus in accordance withthe first preferred embodiment.

FIG. 9 is a cross section of a semiconductor wafer in which a carbonthin film is formed on the surface of a silicon substrate.

FIG. 10 is a schematic view showing a state where the semiconductorwafer in which the carbon thin film is formed is irradiated with flashlight.

FIG. 11 is a view showing a correlation between charge voltage and asheet resistance value.

FIG. 12 is a view schematically showing variation in the decrease offilm thickness of the carbon thin film.

FIG. 13 is a longitudinal section showing a configuration of a heattreatment apparatus in accordance with a second preferred embodiment ofthe present invention.

FIG. 14 is a partially enlarged cross section showing a mechanism forsupplying gas to a chamber in the heat treatment apparatus of FIG. 13.

FIG. 15 is a schematic plan view showing the chamber of the heattreatment apparatus taken along the horizontal plane at the level of agas outlet.

FIG. 16 is another longitudinal section showing the configuration of theheat treatment apparatus of FIG. 13.

FIG. 17 is a block diagram showing a constitution of a controller inaccordance with the second preferred embodiment.

FIG. 18 is a flowchart showing part of an operation flow of processing asemiconductor wafer in accordance with the second preferred embodiment.

FIG. 19 is a flowchart showing process steps for processing thesemiconductor wafer in the heat treatment apparatus in accordance withthe second preferred embodiment.

FIG. 20 is a cross section of a semiconductor wafer immediately after acarbon thin film is formed on the surface of a silicon substrate.

FIG. 21 is a schematic view showing an airflow formed in the chamber ofthe heat treatment apparatus.

FIG. 22 is a cross section of the semiconductor wafer after the carbonthin film is processed.

FIG. 23 is a cross section of the semiconductor wafer in which aplural-layered thin film is formed on the surface of a siliconsubstrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the preferred embodiments of the present invention will bediscussed in detail with reference to the drawings.

The First Preferred Embodiment

First, a general configuration of a heat treatment apparatus inaccordance with the present invention will be outlined. FIG. 1 is alongitudinal section showing a configuration of a heat treatmentapparatus 1 in accordance with the first preferred embodiment of thepresent invention. The heat treatment apparatus 1 is a lamp annealer forirradiating a substantially circular semiconductor wafer W serving as asubstrate with a flash of light so as to heat the semiconductor wafer W.

The heat treatment apparatus 1 comprises a substantially cylindricalchamber 6 for housing the semiconductor wafer W therein and a lamp house5 incorporating a plurality of flash lamps FL. The heat treatmentapparatus 1 further comprises a controller 3 for controlling operatingmechanisms provided in the chamber 6 and in the lamp house 5 to performa heat treatment on the semiconductor wafer W.

The chamber 6 is provided below the lamp house 5 and constituted of achamber side portion 63 having a substantially cylindrical inner walland a chamber bottom portion 62 covering the bottom of the chamber sideportion 63. A space surrounded by the chamber side portion 63 and thechamber bottom portion 62 is defined as a heat treatment space 65. Abovethe heat treatment space 65 is a top opening 60 equipped with andblocked by a chamber window 61.

The chamber window 61 forming the ceiling of the chamber 6 is adisk-shaped member made of quartz and serves as a quartz window thattransmits flash light emitted from the lamp house 5 into the heattreatment space 65. The chamber bottom portion 62 and the chamber sideportion 63, which form the main body of the chamber 6, are made of, forexample, a metal material such as stainless steel having high strengthand high heat resistance, and a ring 631 provided on the upper innerside surface of the chamber side portion 63 is made of an aluminum (Al)alloy or the like having greater durability than stainless steel againstdegradation due to light irradiation.

In order to maintain the hermeticity of the heat treatment space 65, thechamber window 61 and the chamber side portion 63 are sealed with anO-ring. To be more specific, the O-ring is inserted between a lower-sideperipheral portion of the chamber window 61 and the chamber side portion63, and a clamp ring 90 is provided to abut against an upper-sideperipheral portion of the chamber window 61 and to be screwed to thechamber side portion 63, whereby the chamber window 61 is forced ontothe O-ring.

The chamber bottom portion 62 has a plurality of (three, in thispreferred embodiment) support pins 70 extending upright therefromthrough a holder 7 in order to support the semiconductor wafer W fromthe lower surface thereof (the surface opposite to a surface to beirradiated with light from the lamp house 5). The support pins 70 aremade of, for example, quartz and can be replaced easily because thesupport pins 70 are secured from the outside of the chamber 6.

The chamber side portion 63 has a transport opening 66 forloading/unloading of the semiconductor wafer W therethrough. Thetransport opening 66 is openable and closable by a gate valve 185 thatpivots about an axis 662. To the opposite side of the chamber sideportion 63 from the transport opening 66, connected is a gas inletpassage 81 for introducing a process gas into the heat treatment space65. The gas inlet passage 81 has one end connected to a gas inlet buffer83 formed inside the chamber side portion 63 and the other endcommunicating with a gas source 88. At some midpoint in the gas inletpassage 81, interposed are a gas valve 82 and a flow rate regulatingvalve 85. The gas source 88 supplies an inert gas such as nitrogen (N₂)gas, helium (He) gas, or argon (Ar) gas or a reactive gas such as oxygen(O₂) gas or ammonia (NH₃) gas to the gas inlet passage 81. The gassource 88 selectively supplies any one of these gases or supplies amixture of the gases as the process gas. Further, the transport opening66 has an outlet passage 86 formed to exhaust gas from the heattreatment space 65 and connected through a gas valve 87 to a not-shownexhaust mechanism.

FIG. 2 is a cross section of the chamber 6 taken along the horizontalplane at the level of the gas inlet buffer 83. As shown in FIG. 2, thegas inlet buffer 83 is formed to extend over about one third of theinner periphery of the chamber side portion 63 on the opposite side fromthe transport opening 66 shown in FIG. 1. When the gas valve 82 isopened, the process gas is supplied from the gas source 88 to the gasinlet passage 81 and guided to the gas inlet buffer 83, and furthersupplied through a plurality of gas supply holes 84 into the heattreatment space 65. The flow rate of the process gas to be supplied isdetermined by the flow rate regulating valve 85. When the gas valve 87is opened, the atmosphere inside the heat treatment space 65 isexhausted through the outlet passage 86. This causes an airflow of theprocess gas in the heat treatment space 65, which is indicated by thearrows AR4 of FIG. 2.

Referring back to FIG. 1, the heat treatment apparatus 1 furthercomprises the substantially disk-shaped holder 7 for holding thesemiconductor wafer W being rested in a horizontal position inside thechamber 6 and preheating the semiconductor wafer W held thereby prior toirradiation with flash light and a holder elevating mechanism 4 formoving the holder 7 vertically relative to the chamber bottom portion 62which is the bottom of the chamber 6. The holder elevating mechanism 4of FIG. 1 includes a substantially cylindrical shaft 41, a movable plate42, guide members 43 (in the present preferred embodiment, three guidemembers 43 are provided around the shaft 41), a fixed plate 44, a ballscrew 45, a nut 46, and a motor 40. The chamber bottom portion 62, whichis the bottom of the chamber 6, has a substantially circular bottomopening 64 having a diameter smaller than that of the holder 7. Theshaft 41 of stainless steel extends through the bottom opening 64 and isconnected to the underside of the holder 7 (strictly describing, a hotplate 71 of the holder 7) to support the holder 7.

The nut 46 in threaded engagement with the ball screw 45 is fixed to themovable plate 42. The movable plate 42 is movable in a verticaldirection while being slidably guided by the guide members 43 that arefixed to and extend downwardly from the chamber bottom portion 62. Themovable plate 42 is also coupled to the holder 7 through the shaft 41.

The motor 40 is installed on the fixed plate 44 mounted to the lowerends of the guide members 43 and is connected to the ball screw 45 via atiming belt 401. When the holder elevating mechanism 4 moves the holder7 vertically, the motor 40 serving as a driving part rotates the ballscrew 45 under the control of the controller 3 to cause the movableplate 42 fixed to the nut 46 to move along the guide members 43 in thevertical direction. Consequently, the shaft 41 fixed to the movableplate 42 is moved in the vertical direction, and the holder 7 connectedto the shaft 41 is thereby moved up and down smoothly between a transferposition shown in FIG. 1 for transfer of the semiconductor wafer W and aprocessing position shown in FIG. 5 for processing of the semiconductorwafer W.

On the upper surface of the movable plate 42, a mechanical stopper 451of substantially semi-cylindrical shape (the shape formed by cutting acylinder into half along its length) extends upright along the ballscrew 45. Even if any anomalies happen to cause the movable plate 42 tomove up beyond a predetermined upper limit, the top end of themechanical stopper 451 will strike an end plate 452 provided at an endportion of the ball screw 45, whereby the abnormal upward movement ofthe movable plate 42 is prevented. This prevents the holder 7 frommoving up beyond a predetermined position lying under the chamber window61, thus avoiding collision of the holder 7 with the chamber window 61.

The holder elevating mechanism 4 further includes a manual elevator 49for manually moving the holder 7 up and down for the maintenance of theinterior of the chamber 6. The manual elevator 49 includes a handle 491and a rotary shaft 492 and can move the holder 7 up and down by rotatingthe rotary shaft 492 with the handle 491 to thereby rotate the ballscrew 45 connected to the rotary shaft 492 via a timing belt 495.

On the underside of the chamber bottom portion 62, expandable andcontractible bellows 47 that extend downwardly around the shaft 41 areprovided, with their upper ends connected to the underside of thechamber bottom portion 62. The lower ends of the bellows 47 are mountedto a bellows-lower-end plate 471. The bellows-lower-end plate 471 isscrewed to the shaft 41 with a collar member 411. The bellows 47 willcontract when the holder elevating mechanism 4 moves the holder 7upwardly relative to the chamber bottom portion 62, while the bellows 47will expand when the holder elevating mechanism 4 moves the holder 7downwardly. The expansion and contraction of the bellows 47 allows theheat treatment space 65 to be kept air-tight even during the upward anddownward movement of the holder 7.

FIG. 3 is a cross section showing a structure of the holder 7. Theholder 7 has a substantially disk-like shape with a diameter larger thanthat of the semiconductor wafer W. The holder 7 includes the hot plate(heating plate) 71 for performing preheating (what is called assistedheating) of the semiconductor wafer W and a susceptor 72 installed onthe upper surface (the face where the holder 7 holds the semiconductorwafer W) of the hot plate 71. The underside of the holder 7 is, asdescribed previously, connected to the shaft 41 for moving the holder 7up and down. The susceptor 72 is made of quartz (or it may be ofaluminum nitride (AlN) or the like) and has, on its upper surface, pins75 for preventing misalignment of the semiconductor wafer W. Thesusceptor 72 is provided on the hot plate 71, with its underside inface-to-face contact with the upper surface of the hot plate 71. Thesusceptor 72 is thus capable of diffusing and transmitting heat energyfrom the hot plate 71 to the semiconductor wafer W placed on the uppersurface of the susceptor 72 and is cleanable during the maintenance bybeing removed from the hot plate 71.

The hot plate 71 includes an upper plate 73 and a lower plate 74 bothmade of stainless steel. Resistance heating wires 76, such as nichromewires, for heating the hot plate 71 are installed between the upperplate 73 and the lower plate 74, and a space between the upper plate 73and the lower plate 74 is filled and sealed with electrically conductivebrazing nickel (Ni). Respective end portions of the upper plate 73 andthe lower plate 74 are brazed to each other.

FIG. 4 is a plan view showing the hot plate 71. As shown in FIG. 4, thehot plate 71 has a disk-like zone 711 and an annular zone 712 that areconcentrically arranged in the central portion of an area facing thesemiconductor wafer W being held, and four zones 713 to 716 formed bydividing a substantially annular area around the zone 712 into fourequal sections in a circumferential direction. Each pair of adjacentzones has a slight gap formed therebetween. The hot plate 71 is furtherprovided with three through holes 77 through which the support pins 70are inserted, respectively. The three through holes 77 arecircumferentially spaced apart from one another every 120 degrees in agap between the zones 711 and 712.

In each of the six zones 711 to 716, the resistance heating wires 76independent of one another are so provided as to circulate around thezone to form an individual heater. The heater incorporated in each zoneindividually heats the zone. The semiconductor wafer W held by theholder 7 is heated by those heaters incorporated in the six zones 711 to716. Each of the zones 711 to 716 has a sensor 710 for measuring thetemperature of the zone with a thermocouple. Each sensor 710 isconnected to the controller 3 through the inside of the substantiallycylindrical shaft 41.

For heating the hot plate 71, the controller 3 controls the amount ofpower to be supplied to the resistance heating wires 76 provided in eachzone so that the temperature of each of the six zones 711 to 716measured by the sensor 710 becomes a predetermined preset temperature.The controller 3 uses PID (Proportional Integral Derivative) control forthe temperature control of each zone. In the hot plate 71, thetemperature of each of the zones 711 to 716 is continuously measureduntil the heat treatment on the semiconductor wafer W is completed (or,when there are a plurality of semiconductor wafers W to be treated insuccession, until the heat treatment on all the semiconductor wafers Wis completed), and the amount of power to be supplied to the resistanceheating wires 76 provided in each zone is controlled on an individualbasis, i.e., the temperature of the heater incorporated in each zone iscontrolled individually, whereby the temperature of each zone is kept ata set temperature. The set temperature of each zone can be changed onlyby an individually determined offset value from a reference temperature.

The resistance heating wires 76 provided in each of the six zones 711 to716 are connected to a plate power supply 98 (see FIG. 6) via a powerline passing through the inside of the shaft 41. On the way from theplate power supply 98 to each zone, the power line from the plate powersupply 98 is installed within a stainless tube filled with an insulatorsuch as magnesia (magnesium oxide) so as to be electrically insulatedfrom the other lines. The inside of the shaft 41 is open to theatmosphere.

The lamp house 5 is provided above the chamber 6. The lamp house 5comprises, inside a case 51, a light source including a plurality of (inthis preferred embodiment, thirty) xenon flash lamps FL, and a reflector52 provided to cover over the light source. The lamp house 5 also has alamp light radiating window 53 mounted to the bottom of the case 51. Thelamp light radiating window 53 forming the floor portion of the lamphouse 5 is a plate-like member made of quartz. Since the lamp house 5 isprovided above the chamber 6, the lamp light radiating window 53 isopposed to the chamber window 61. The lamp house 5 emits flash lightfrom the flash lamps FL through the lamp light radiating window 53 andthe chamber window 61 to the semiconductor wafer W held by the holder 7in the chamber 6, to thereby heat the semiconductor wafer W.

The plurality of flash lamps FL, each of which is a rod-shaped lamphaving a long-length cylindrical shape, are arranged in a plane withtheir longitudinal directions in parallel with one another along themain surface (i.e., along the horizontal direction) of the semiconductorwafer W held by the holder 7. The plane defined by the array of theflash lamps FL is accordingly a horizontal plane. The area of the planedefined by the array of the plurality of flash lamps FL is at leastlarger than the area of the semiconductor wafer W held by the holder 7.

The xenon flash lamp FL comprises a rod-like glass tube (discharge tube)which is filled with xenon gas and provided with an anode and a cathodeconnected to a capacitor at its respective end portions and a triggerelectrode coiled around the outer peripheral surface of the glass tube.Since the xenon gas is an electrical insulator, no electricity flows inthe glass tube in a normal state even if electric charges areaccumulated in the capacitor. In a case where high voltage is applied tothe trigger electrode to break the insulation, however, the electricityaccumulated in the capacitor instantaneously flows into the glass tubeand light is emitted by excitation of atoms or molecules of the xenon atthat time. Such a xenon flash lamp FL, in which the electrostatic energyaccumulated in the capacitor in advance is converted into an extremelyshort light pulse ranging from 0.1 to 100 milliseconds, has acharacteristic feature of being capable of emitting extremely intenselight as compared with a light source of successive lighting. The lightemission time of the flash lamp FL can be controlled by the coilconstant of a lamp power supply 99 (see FIG. 6) for supplying the flashlamps FL with power.

The reflector 52 is provided above the plurality of flash lamps FL tocover over all those flash lamps FL. The fundamental function of thereflector 52 is to reflect the flash light emitted from the plurality offlash lamps FL toward the holder 7. The reflector 52 is an aluminumalloy plate, and its surface (facing the flash lamps FL) is roughened byabrasive blasting to produce a satin finish thereon. Such surfaceroughing is required, because if the reflector 52 has a perfect mirrorsurface, the intensity of the reflected light from the plurality offlash lamps FL will exhibit a regular pattern, which can causedeterioration in the uniformity of the surface temperature distributionin the semiconductor wafer W.

The controller 3 controls the aforementioned various operatingmechanisms provided in the heat treatment apparatus 1. FIG. 6 is a blockdiagram showing a constitution of the controller 3. The hardwareconfiguration of the controller 3 is similar to that of a generalcomputer. Specifically, the controller 3 has a constitution in which aCPU 31 for performing various computations, a ROM or read-only memory 32for storing basic programs therein, a RAM or readable/writable memory 33for storing various pieces of information therein, a magnetic disk 34for storing control software, data or the like therein are connected toa bus line 39.

To the bus line 39, the motor 40 of the holder elevating mechanism 4 formoving the holder 7 up and down in the chamber 6, the lamp power supply99 for supplying the flash lamps FL with power, the gas valves 82 and 87for supplying and exhausting the process gas to/from the chamber 6, theflow rate regulating valve 85, the gate valve 185 for opening andclosing the transport opening 66, the plate power supply 98 forsupplying the zones 711 to 716 of the hot plate 71 with power, and thelike are electrically connected. The CPU 31 of the controller 3 executesthe control software stored in the magnetic disk 34 to control theseoperation mechanisms, to thereby allow the heat treatment on thesemiconductor wafer W to proceed.

Further, to the bus line 39, a display part 35 and an input part 36 arealso electrically connected. The display part 35 includes, e.g., aliquid crystal display (LCD) and the like and displays various pieces ofinformation such as a processing result, details of a recipe and thelike. The input part 36 includes, e.g., a keyboard, a mouse and the likeand receives inputs such as commands, parameters and the like. Anoperator of this apparatus can input commands, parameters and the likeby using the input part 36 while checking the contents displayed on thedisplay part 35. Combining the display part 35 and the input part 36, atouch panel may be used.

The heat treatment apparatus 1 further comprises, in addition to theabove constituent elements, various cooling mechanisms to prevent anexcessive temperature rise in the chamber 6 and in the lamp house 5 dueto heat energy generated by the flash lamps FL and the hot plate 71during the heat treatment on the semiconductor wafer W. For example, awater cooled tube (not shown) is provided on the chamber side portion 63and the chamber bottom portion 62 of the chamber 6. The lamp house 5forms an air cooling structure in which a gas supply pipe 55 and anexhaust pipe 56 are provided to thereby form a gas flow therein and toexhaust heat (see FIGS. 1 and 5). Air is supplied also to a gap betweenthe chamber window 61 and the lamp light radiating window 53, to therebycool the lamp house 5 and the chamber window 61.

Now, a procedure for processing a semiconductor wafer W will bediscussed. FIG. 7 is a flowchart showing part of an operation flow forprocessing the semiconductor wafer W in accordance with the firstpreferred embodiment. First, patterns are formed on a surface of thesilicon substrate 11 (see FIG. 9) by using a photolithography techniqueand impurities (ions) such as boron (B) or arsenic (As) are implantedinto a source/drain region (Step S1). The impurity implantation isperformed by ion implantation.

Subsequently, a carbon (C) thin film 12 is formed on the surface of thesilicon substrate 11 implanted with the impurities (Step S2). Forformation of the carbon thin film 12, various well-known techniques maybe adopted. For example, the carbon thin film 12 may be formed by plasmadeposition. FIG. 9 is a cross section of a semiconductor wafer W inwhich the carbon thin film 12 is formed on the surface of the siliconsubstrate 11. In the first preferred embodiment, on the surface of thesilicon substrate 11 implanted with the impurities by ion implantation,the amorphous carbon thin film 12 is formed by plasma deposition.Further, in the first preferred embodiment, the film thickness t (theinitial value of the film thickness) of the amorphous carbon thin film12 formed on the surface of the silicon substrate 11 is 70 nm.

Next, the heat treatment apparatus 1 performs light irradiation heattreatment on the semiconductor wafer W in which the carbon thin film 12is formed (Step S3). The light irradiation heat treatment performed onthe semiconductor wafer W by the heat treatment apparatus 1 will bediscussed later in more detail.

After the light irradiation heat treatment is finished by the heattreatment apparatus 1, cleaning of the semiconductor wafer W isperformed (Step S4). This cleaning process includes so-called SPMcleaning (using a mixture of sulfuric acid and oxygenated water) and APMcleaning (using a mixture of aqueous ammonia and oxygenated water). Byperforming this cleaning process, the carbon thin film 12 is completelyremoved from the surface of the silicon substrate 11. In thisspecification, the “semiconductor wafer W” refers both to the siliconsubstrate 11 with no thin film formed on its surface and the siliconsubstrate 11 with a thin film 12 formed on its surface.

FIG. 8 is a flowchart showing a procedure for processing thesemiconductor wafer W in the heat treatment apparatus 1 in accordancewith the first preferred embodiment. The procedure of FIG. 8 forprocessing the semiconductor wafer W is carried out by the controller 3controlling the operation mechanisms of the heat treatment apparatus 1.

First, the holder 7 moves down from the processing position shown inFIG. 5 to the transfer position shown in FIG. 1 (Step S20). The“processing position” is a position where the holder 7 is located whenthe semiconductor wafer W is irradiated with light from the flash lampsFL, which is the position of the holder 7 in the chamber 6 shown in FIG.5. The “transfer position” is a position where the holder 7 is locatedwhen the semiconductor wafer W is loaded or unloaded into/from thechamber 6, which is the position of the holder 7 in the chamber 6 shownin FIG. 1. The reference position of the holder 7 in the heat treatmentapparatus 1 is the processing position. Before the processing, theholder 7 is located at the processing position, and when the processingstarts, the holder 7 moves down to the transfer position.

The holder 7 moves up and down relative to the support pins 70 fixed tothe chamber 6. As shown in FIG. 1, moving down to the transfer position,the holder 7 comes close to the chamber bottom portion 62 and therespective tips of the support pins 70 penetrate the holder 7 andprotrude over the holder 7.

Next, after the holder 7 moves down to the transfer position, the gasvalve 82 is opened and an inert gas (nitrogen gas in this preferredembodiment) is thereby supplied into the heat treatment space 65 of thechamber 6 from the gas source 88. At the same time, the gas valve 87 isopened and the gas is thereby exhausted from the heat treatment space 65(Step S21). The nitrogen gas supplied into the chamber 6 flows in theheat treatment space 65 in the direction indicated by the arrows AR4 ofFIG. 2 from the gas inlet buffer 83 and is exhausted through the outletpassage 86 and the gas valve 87 by utility exhaust. Part of the nitrogengas supplied into the chamber 6 is exhausted also from an exhaust port(not shown) provided inside the bellows 47.

Subsequently, the gate valve 185 is opened to open the transport opening66, and the semiconductor wafer W with the carbon thin film 12 formed onits surface is loaded into the chamber 6 through the transport opening66 by a transfer robot provided outside this apparatus and placed on theplurality of support pins 70 (Step S22). After the semiconductor wafer Wis loaded into the chamber 6, the transport opening 66 is closed by thegate valve 185. Then, the holder elevating mechanism 4 moves the holder7 from the transfer position up to the processing position near thechamber window 61 (Step S23). In the course of moving the holder 7 upfrom the transfer position, the semiconductor wafer W is passed from thesupport pins 70 to the susceptor 72 of the holder 7 and placed on theupper surface of the susceptor 72 to be held thereon. When the holder 7moves up to the processing position, the semiconductor wafer W held bythe susceptor 72 is also held at the processing position.

Each of the six zones 711 to 716 of the hot plate 71 is already heatedup to a predetermined temperature by the heater (the resistance heatingwires 76) which is individually incorporated within the zone (betweenthe upper plate 73 and the lower plate 74). The holder 7 is moved up tothe processing position and the semiconductor wafer W comes into contactwith the holder 7, whereby the semiconductor wafer W is preheated by theheaters incorporated in the hot plate 71 and the temperature thereofincreases gradually (Step S24).

The preheating of the semiconductor wafer W at the processing positionfor about 60 seconds increases the temperature of the semiconductorwafer W up to a preheating temperature T1 which is set in advance. Thepreheating temperature T1 is set ranging from about 200° C. to about600° C., preferably from about 350° C. to about 550° C., at which thereis no apprehension that the impurities implanted in the semiconductorwafer W might be diffused by heat. The distance between the holder 7 andthe chamber window 61 is arbitrarily adjustable by controlling theamount of rotation of the motor 40 of the holder elevating mechanism 4.

Concurrently with the preheating of the semiconductor wafer W performedat the processing position, oxygen gas is introduced into the heattreatment space 65 of the chamber 6 (Step S25). Specifically, the oxygengas is supplied into the heat treatment space 65 from the gas source 88through the gas inlet passage 81. At that time, only the oxygen gas maybe supplied or a mixed gas of nitrogen gas and oxygen gas may besupplied. The flow rate of the oxygen gas to be supplied into the heattreatment space 65 from the gas source 88 is controlled by thecontroller 3 controlling the gas valve 82 and the flow rate regulatingvalve 85. In the first preferred embodiment, by the supply of the oxygengas in Step S25, the concentration of oxygen in the heat treatment space65 is set to be 90% or more.

After the preheating time for about 60 seconds has elapsed and theoxygen concentration in the chamber 6 becomes 90% or more, the flashlight is emitted from the flash lamps FL of the lamp house 5 toward thesemiconductor wafer W under the control of the controller 3 in the statewhere the holder 7 is located at the processing position (Step S26). Atthat time, part of the flash light emitted from the flash lamps FLtravels directly to the holder 7 inside the chamber 6. The remainder ofthe flash light is reflected by the reflector 52, and the reflectedlight travels to the inside of the chamber 6. With such emission of theflash light, the flash heating is performed on the semiconductor waferW. The flash heating, which is achieved by emission of the flash lightfrom the flash lamps FL, can raise the surface temperature of thesemiconductor wafer W in a short time.

Specifically, the flash light emitted from the flash lamps FL of thelamp house 5 is an extremely short and intense flash of light emittedfor a period of time not shorter than 0.1 milliseconds and not longerthan 100 milliseconds because the previously stored electrostatic energyis converted into such an ultrashort light pulse. The surfacetemperature of the semiconductor wafer W (exactly, the surfacetemperature of the carbon thin film 12) subjected to the flash heatingby emission of flash light from the flash lamps FL instantaneously risesto a treatment temperature T2, and after the impurities implanted in thesemiconductor wafer W are activated, the surface temperature fallsquickly. In the heat treatment apparatus 1, since the surfacetemperature of the semiconductor wafer W can be increased and decreasedin an extremely short time, activation of the impurities implanted inthe semiconductor wafer W can be achieved while the diffusion of theimpurities due to heat is suppressed. Since the time period required forthe activation of the impurities is extremely short as compared with thetime period required for the thermal diffusion of the impurities, theactivation is completed even in a short time ranging from about 0.1 toabout 100 milliseconds during which no diffusion occurs.

FIG. 10 is a schematic view showing a state where the semiconductorwafer W with the carbon thin films 12 formed thereon is irradiated withflash light. As the film thickness of the carbon thin film 12 formed onthe surface of the semiconductor wafer W becomes larger, the surfacereflectance of the semiconductor wafer W decreases, and in the firstpreferred embodiment, when the film thickness is 70 nm, the surfacereflectance is about 60%. The decrease in the surface reflectance meansthe increase in the absorptivity of flash light in the semiconductorwafer W, and more specifically, it means the increase in theabsorptivity of flash light in the carbon thin film 12. The spectraldistribution of radiation of flash light from the xenon flash lamps FLranges from ultraviolet to near-infrared regions and the flash lighthardly passes through the silicon substrate 11.

The decrease in the surface reflectance of the semiconductor wafer Wwith the increase in the film thickness of the carbon thin film 12 iscaused by the increase in the absorptivity of flash light in the carbonthin film 12 with the increase in the film thickness thereof.Specifically, when the carbon thin film 12 becomes thick to some degreeor more, part of the flash light emitted as indicated by the arrow AR10of FIG. 10 is absorbed by the thin film 12. The absorptivity becomeslarger as the film thickness of the thin film 12 becomes larger. Heat isgenerated on the surface of the carbon thin film 12 which has absorbedthe flash light and the heat is transferred to the surface of thesilicon substrate 11 as indicated by the arrow AR11.

Thus, the carbon thin film 12 having a given film thickness or morefunctions as a light absorption film to increase the absorptivity offlash light in the semiconductor wafer W. As a result of increasing theabsorptivity of flash light in the semiconductor wafer W, the attainedsurface temperature of the semiconductor wafer W during irradiation withthe flash light (strictly describing, the attained surface temperatureof the surface of the silicon substrate 11 implanted with theimpurities) increases as compared with that in the case where no thinfilm 12 is formed, and this allows better activation of the impuritiesto be achieved.

FIG. 11 is a view showing a correlation between charge voltage and thesheet resistance value. The charge voltage indicated by the horizontalaxis is voltage to be applied to the capacitor of the lamp power supply99 (see FIG. 6) which supplies power to the flash lamps FL, serving asan index indicating the magnitude of the energy of flash light emittedfrom the flash lamps FL. The sheet resistance value Rs indicated by thevertical axis serves as an index indicating the degree of activation ofthe impurities, and a lower sheet resistance value indicates highertemperature of the heated surface of the semiconductor wafer W andexecution of better activation of the impurities. In FIG. 11, the solidline indicates the correlation in the semiconductor wafer W of the firstpreferred embodiment with the carbon thin film 12 formed thereon and thedotted line indicates the correlation in the semiconductor wafer W withno carbon thin film 12 formed thereon.

As shown in FIG. 11, if the same charge voltage is applied, the sheetresistance value becomes lower and in other words, the surfacetemperature of the semiconductor wafer W becomes higher when the carbonthin film 12 is formed. The difference in the sheet resistance value ismore particularly remarkable when the charge voltage is lower, and thesemiconductor wafer W with the carbon thin film 12 formed thereon asshown in the first preferred embodiment can achieve a sufficiently lowsheet resistance value even if a low charge voltage is applied. In otherwords, when the carbon thin film 12 is formed on the semiconductor waferW, the surface temperature can be increased to be still higher and thesheet resistance value can be decreased even if the energy of the flashlight from the flash lamps FL is relatively small.

As shown in FIG. 10, the flash light emitted from the flash lamps FL isonce absorbed by the carbon thin film 12 which is uniformly formed tocause heat in the thin film 12, and then the heat is transferred to thesurface of the silicon substrate 11 as indicated by the AR11. Therefore,even if there is variation of the absorptivity in the surface of thesilicon substrate 11 due to formation of patterns, the variation of theabsorptivity can be eased as compared with the case where no thin filmis formed, and the surface of the silicon substrate 11 implanted withthe impurities is thereby uniformly heated.

In the first preferred embodiment, the oxygen concentration in thechamber 6 is set to 90% or more when flash light is emitted from theflash lamps FL. The carbon of the thin film 12 heated by irradiationwith flash light reacts with oxygen to produce carbon dioxide (CO₂) orcarbon monoxide (CO). The carbon of the thin film 12 is thus vaporized,being consumed, and the film thickness of the thin film 12 decreases. Inother words, the carbon thin film 12 is removed by introduction ofoxygen into the chamber 6 while serving as a light absorption filmduring the irradiation with flash light. Since the produced oxide ofcarbon is gas, the gas is exhausted together with the atmospheric gas inthe chamber 6 through the outlet passage 86 and the gas valve 87 to theoutside of the heat treatment apparatus 1.

The rate of decrease in the film thickness of the thin film 12 due toconsumption of carbon during the irradiation with flash light is notuniform in the plane of the semiconductor wafer W. In other words, theintensity of the flash light emitted from the flash lamps FL through thelamp light radiation window 53 and the chamber window 61 to the heattreatment space 65 is not necessarily uniform and this causes variationof the intensity distribution in the plane of the semiconductor wafer W.For this reason, as a result of causing variation in the inplanetemperature distribution of the thin film 12, the rate of decrease inthe film thickness becomes nonuniform.

FIG. 12 is a view schematically showing variation in the decrease offilm thickness of the carbon thin film 12. It is assumed that the flashlight emitted from the flash lamps FL through the lamp light radiationwindow 53 and the chamber window 61 into the heat treatment space 65includes such less intense flash light as indicated by the arrow AR12and such more intense flash light as indicated by the arrow AR13. Inthis case, in the surface of the carbon thin film 12, an area irradiatedwith the more intense flash light is heated to have higher temperaturethan another area irradiated with the less intense flash light.Consequently, the reaction of the ambient atmosphere with oxygen becomesmore active and the rate of decrease in the film thickness becomeslarger in the area irradiated with the more intense flash light than thearea irradiated with the less intense flash light, and the filmthickness of the carbon thin film 12 thus becomes uniform as shown inFIG. 12.

The absorptivity of flash light in the carbon thin film 12 depends onthe film thickness, and specifically, the absorptivity increases as thefilm thickness becomes larger. Therefore, as the result that the filmthickness of the thin film 12 thus becomes nonuniform, the remainingfilm thickness becomes larger and the absorptivity of flash lightincreases in the area irradiated with the less intense flash light thanthe area irradiated with the more intense flash light. In an areairradiated with flash light of higher intensity, the film thickness ofthe thin film 12 becomes smaller and the absorptivity of flash lightdecreases, and consequently, the surface temperature of the areadecreases and the inplane temperature distribution becomes uniform inthe thin film 12 on the whole. In other words, the nonuniformity in thefilm thickness of the thin film 12 caused by the difference in theintensity of flash light functions to cancel the variation in theinplane temperature distribution. If the inplane temperaturedistribution becomes uniform in the thin film 12 on the whole, thesurface of the silicon substrate 11 implanted with the impurities can bealso heated uniformly.

After the lapse of predetermined time (several seconds) from the end ofthe flash heating, nitrogen gas is supplied again into the heattreatment space 65 from the gas source 88 while the gas containing theoxygen gas is exhausted from the heat treatment space 65 through theoutlet passage 86. The atmosphere in the chamber 6 is therebysubstituted with the nitrogen gas (Step S27).

Then, the holder 7 is moved down again to the transfer position shown inFIG. 1 by the holder elevating mechanism 4, and the semiconductor waferW is passed from the holder 7 to the support pins 70 (Step S28).Subsequently, the gate valve 185 opens the transport opening 66 havingbeen closed, and the transfer robot provided outside this apparatusunloads the semiconductor wafer W rested on the support pins 70. Thus,the flash heat treatment (annealing process) on the semiconductor waferW in the heat treatment apparatus 1 is completed (Step S29).

As discussed above, in the first preferred embodiment, formation of thecarbon thin film 12 on the surface of the semiconductor wafer W allowsthe carbon thin film 12 to absorb the flash light. Absorbing the flashlight causes the temperature of the carbon thin film 12 to rise, and itis thereby possible to increase the surface temperature of the siliconsubstrate 11 implanted with the impurities to be still higher anddecrease the sheet resistance value as compared with the case where nothin film 12 is formed.

Particularly, if the carbon thin film 12 is formed on the surface of thesemiconductor wafer W, a sufficiently low sheet resistance value can beachieved even with a low charge voltage as shown in FIG. 11. Therefore,without increasing the loads of the flash lamps FL and the lamp powersupply 99, a low sheet resistance value can be achieved.

Since the oxygen concentration in the chamber 6 is set to 90% or moreand the semiconductor wafer W with carbon thin film 12 formed thereon isirradiated with the flash light, the carbon of the heated thin film 12is oxidized and thus vaporized, thereby being consumed. This allowsremoval of the carbon thin film 12 to proceed during the flash heating,and the remaining film of carbon can be removed only by the normal SPMcleaning and APM cleaning in the subsequent cleaning process (Step S4).If the flash light is emitted without introduction of the oxygen gasinto the chamber 6, since the carbon of the thin film 12 is notconsumed, the original film thickness is generally maintained even afterthe flash heating. In this case, the thin film 12 is not fully removedonly by the normal SPM cleaning and APM cleaning and an ashing processis additionally needed before the cleaning process of Step S4. As shownin the first preferred embodiment, if oxygen gas is introduced into thechamber 6 to set the oxygen concentration therein to 90% or more duringemission of flash light, the removal of the thin film 12 can be alsoachieved by the irradiation with flash light at the same time, andtherefore, no ashing process is needed and the remaining film can bereliably removed only by the normal cleaning process. The carbon thinfilm 12 is not entirely vaporized during the emission of flash light,and the remaining film also serves as an antioxidizing film for thesurface of the silicon substrate 11.

Further, in the first preferred embodiment, if there is variation in theintensity of the flash light emitted from the flash lamps FL, thiscauses variation in the rate of decrease in the film thickness of thethin film 12, which makes the film thickness thereof nonuniform, but thenonuniformity in the film thickness functions to cancel the variation inthe inplane temperature distribution of the semiconductor wafer W.Specifically, in an area irradiated with flash light of higherintensity, the film thickness of the thin film 12 becomes smaller andthe absorptivity of flash light decreases, and consequently, the surfacetemperature of the area decreases and the inplane temperaturedistribution becomes uniform in the surface of the semiconductor wafer Won the whole.

When the flash heat treatment is performed on the semiconductor wafer Wwith the carbon thin film 12 formed thereon, there may be deposition ofcarbon-based contaminants on the inside of the chamber 6. If there isdeposition of such contaminants, oxygen gas is introduced into thechamber 6 to set the oxygen concentration therein to 90% or more,without housing the semiconductor wafer W in the chamber 6, and then theflash lamps FL emit flash light. In other words, idle flashing isperformed while the oxygen concentration in the chamber 6 is kept at 90%or more. Like the flash heat treatment on the semiconductor wafer W,such idle flashing is also implemented by the controller 3 controllingthe operation mechanisms (the gas valves 82 and 87, the flow rateregulating valve 85, the lamp power supply 99, and the like) of the heattreatment apparatus 1. By emitting the flash light from the flash lampsFL with the oxygen concentration in the chamber 6 kept at 90% or more,without housing the semiconductor wafer W in the chamber 6, thecarbon-based contaminants are oxidized and thus removed.

In other words, by performing the idle flashing with the oxygenconcentration in the chamber 6 kept at 90% or more, cleaning of theinside of the chamber 6 is achieved.

The Second Preferred Embodiment

Now, the second preferred embodiment of the present invention will bediscussed. FIG. 13 is a longitudinal section showing a configuration ofa heat treatment apparatus 1 in accordance with the second preferredembodiment of the present invention. The heat treatment apparatus 1 is alamp annealer for irradiating a substantially circular semiconductorwafer W serving as a substrate with a flash of light so as to heat thesemiconductor wafer W. The constituent elements identical to those inthe first preferred embodiment are represented by the same referencesigns.

The heat treatment apparatus 1 comprises a substantially cylindricalchamber 6 for housing the semiconductor wafer W therein and a lamp house5 incorporating a plurality of flash lamps FL. The heat treatmentapparatus 1 further comprises a controller 3 for controlling operatingmechanisms provided in the chamber 6 and in the lamp house 5 to performa heat treatment on the semiconductor wafer W.

The chamber 6 is provided below the lamp house 5 and constituted of achamber side portion 63 having a substantially cylindrical inner walland a chamber bottom portion 62 covering the bottom of the chamber sideportion 63. A space surrounded by the chamber side portion 63 and thechamber bottom portion 62 is defined as a heat treatment space 65. Abovethe heat treatment space 65 is a top opening 60 equipped with andblocked by a chamber window 61.

The chamber window 61 forming the ceiling of the chamber 6 is adisk-shaped member made of quartz and serves as a quartz window thattransmits flash light emitted from the lamp house 5 into the heattreatment space 65. The chamber bottom portion 62 and the chamber sideportion 63, which form the main body of the chamber 6, are made of, forexample, a metal material such as stainless steel having high strengthand high heat resistance, and a ring 631 provided on the upper innerside surface of the chamber side portion 63 is made of an aluminum (Al)alloy or the like having greater durability than stainless steel againstdegradation due to light irradiation.

In order to maintain the hermeticity of the heat treatment space 65, thechamber window 61 and the chamber side portion 63 are sealed with anO-ring. To be more specific, the O-ring is inserted between a lower-sideperipheral portion of the chamber window 61 and the chamber side portion63, and a clamp ring 90 is provided to abut against an upper-sideperipheral portion of the chamber window 61 and to be screwed to thechamber side portion 63, whereby the chamber window 61 is forced ontothe O-ring.

The chamber bottom portion 62 has a plurality of (three, in thispreferred embodiment) support pins 70 extending upright therefromthrough a holder 7 in order to support the semiconductor wafer W fromthe lower surface thereof (the surface opposite to a surface to beirradiated with light from the lamp house 5). The support pins 70 aremade of, for example, quartz and can be replaced easily because thesupport pins 70 are secured from the outside of the chamber 6.

The chamber side portion 63 has a transport opening 66 forloading/unloading of the semiconductor wafer W therethrough. Thetransport opening 66 is openable and closable by a gate valve 185 thatpivots about an axis 662. When the gate valve 185 closes the transportopening 66, the heat treatment space 65 becomes a sealed space. When thegate valve 185 opens the transport opening 66, the loading/unloading ofthe semiconductor wafer W to/from the heat treatment space 65 becomespossible.

To the chamber side portion 63, connected is a gas inlet passage 81 forintroducing a process gas into the heat treatment space 65. The gasinlet passage 81 has a tip end connected to a gas inlet buffer 83 formedinside the chamber side portion 63 and a base end communicating with agas source 88. At some midpoint in the gas inlet passage 81, interposedare a gas valve 82 and a flow rate regulating valve 85. The gas source88 supplies an inert gas such as nitrogen (N₂) gas, helium (He) gas, orargon (Ar) gas or a reactive gas such as oxygen (O₂) gas, ammonia (NH₃)gas, or ozone (O₃) gas to the gas inlet passage 81. The gas source 88selectively supplies any one of these gases or supplies a mixture of thegases as the process gas.

FIG. 14 is a partially enlarged cross section showing a mechanism forsupplying gas to the chamber 6. In FIG. 14, the support pins 70 are notshown. As described above, the ring 631 made of an aluminum alloy havingexcellent resistance to flash is engaged in the upper inner side surfaceof the chamber side portion 63 made of stainless steel. By engaging thering 631 in the chamber side portion 63, as shown in FIG. 14, a gasoutlet 89 is formed between the lower end of the ring 631 and thechamber side portion 63. FIG. 15 is a schematic plan view showing thechamber 6 taken along the horizontal plane at the level of the gasoutlet 89. The gas outlet 89 formed between the ring 631 and the chamberside portion 63 is a slit formed in a ring shape along the horizontaldirection. The ring-shaped slit-like gas outlet 89 communicates with thegas inlet buffer 83 formed inside the chamber side portion 63. The gasinlet buffer 83 communicates with three ends of the gas inlet passage81. Specifically, the tip portion of the gas inlet passage 81 branchesinto three, which are connected to the gas inlet buffer 83. Thethree-branched tip portions of the gas inlet passage 81 are connected tothe gas inlet buffer 83 at equal intervals (e.g., at intervals of 120degrees) along the circumferential direction of the cylinder of thechamber side portion 63.

By opening the gas valve 82, a process gas is supplied from the gassource 88 to the gas inlet passage 81, being guided to the gas inletbuffer 83 from the three directions. The flow rate of the process gas tobe supplied is determined by the flow rate regulating valve 85. Theprocess gas having flowed into the gas inlet buffer 83 flows, spreadingin the gas inlet buffer 83 having passage resistance lower than that ofthe gas outlet 89, while being uniformly discharged through the gasoutlet 89 out into the heat treatment space 65.

Referring back to FIG. 13, the heat treatment apparatus 1 furthercomprises the substantially disk-shaped holder 7 for holding thesemiconductor wafer W being rested in a horizontal position inside thechamber 6 and preheating the semiconductor wafer W held thereby prior toirradiation with flash light and a holder elevating mechanism 4 formoving the holder 7 vertically relative to the chamber bottom portion 62which is the bottom of the chamber 6. The constitution and operation ofthe holder elevating mechanism 4 shown in FIG. 13 are the same as thosein the first preferred embodiment, and detailed description thereof willbe omitted.

On the underside of the chamber bottom portion 62, expandable andcontractible bellows 47 that extend downwardly around the shaft 41 areprovided, with their upper ends connected to the underside of thechamber bottom portion 62. The lower ends of the bellows 47 are mountedto a bellows-lower-end plate 471. The bellows-lower-end plate 471 isscrewed to the shaft 41 with a collar member (not shown). The bellows 47will contract when the holder elevating mechanism 4 moves the holder 7upwardly relative to the chamber bottom portion 62, while the bellows 47will expand when the holder elevating mechanism 4 moves the holder 7downwardly. The expansion and contraction of the bellows 47 allows theheat treatment space 65 to be kept air-tight even during the upward anddownward movement of the holder 7.

The bellows-lower-end plate 471 is provided with a gas exhaust outlet472 for exhausting gas from the heat treatment space 65. The gas exhaustoutlet 472 is provided immediately below a bottom opening 64, in otherwords, near the center of the bottom of the chamber 6. The gas exhaustoutlet 472 communicates with a gas exhaust pump 474 through a gas valve473 and a flow rate regulating valve 475. When the gas valve 473 isopened while the gas exhaust pump 474 is operated, the gas in thechamber 6 is exhausted to the outside of the chamber 6 through thebottom opening 64 and the gas exhaust outlet 472. The transport opening66 is provided with an outlet passage 86 for exhausting the gas from theheat treatment space 65, which communicates with a not-shown exhaustmechanism via the gas valve 87. The exhaust mechanism may be the gasexhaust pump 474.

When the process gas is discharged from the gas outlet 89 into the heattreatment space 65 inside the chamber 6 while the atmosphere isexhausted from the chamber 6 through the gas exhaust outlet 472, a flowof the process gas discharged from the inside of the chamber sideportion 63 toward the central portion of the chamber bottom portion 62is caused in the heat treatment space 65.

The constitution of the holder 7 is the same as that in the firstpreferred embodiment (see FIGS. 3 and 4). The constitution of the lamphouse 5 and the configuration of the incorporated xenon flash lamps FLare absolutely the same as those in the first preferred embodiment.

The controller 3 controls the aforementioned various operatingmechanisms provided in the heat treatment apparatus 1. FIG. 17 is ablock diagram showing a constitution of the controller 3. The hardwareconfiguration of the controller 3 is similar to that of a generalcomputer. Specifically, the controller 3 has a constitution in which aCPU 31 for performing various computations, a ROM or read-only memory 32for storing basic programs therein, a RAM or readable/writable memory 33for storing various pieces of information therein, a magnetic disk 34for storing control software, data or the like therein are connected toa bus line 39.

To the bus line 39, a motor 40 of the holder elevating mechanism 4 formoving the holder 7 up and down in the chamber 6, a lamp power supply 99for supplying the flash lamps FL with power, the gas valves 82, 87, and473 for supplying and exhausting the process gas to/from the chamber 6,the flow rate regulating valves 85 and 475, the gate valve 185 foropening and closing the transport opening 66, a plate power supply 98for supplying zones 711 to 716 of the hot plate 71 with power, the gasexhaust pump 474, and the like are electrically connected. The CPU 31 ofthe controller 3 executes the control software stored in the magneticdisk 34 to control these operation mechanisms, to thereby allow the heattreatment on the semiconductor wafer W to proceed.

Further, to the bus line 39, a display part 35 and an input part 36 arealso electrically connected. The display part 35 includes, e.g., aliquid crystal display (LCD) and the like and displays various pieces ofinformation such as a processing result, details of a recipe and thelike. The input part 36 includes, e.g., a keyboard, a mouse and the likeand receives inputs such as commands, parameters and the like. Anoperator of this apparatus can input commands, parameters and the likeby using the input part 36 while checking the contents displayed on thedisplay part 35. Combining the display part 35 and the input part 36, atouch panel may be used.

The heat treatment apparatus 1 further comprises, in addition to theabove constituent elements, various cooling mechanisms to prevent anexcessive temperature rise in the chamber 6 and in the lamp house 5 dueto heat energy generated by the flash lamps FL and the hot plate 71during the heat treatment on the semiconductor wafer W. For example, awater cooled tube (not shown) is provided on the chamber side portion 63and the chamber bottom portion 62 of the chamber 6. The lamp house 5forms an air cooling structure in which a gas supply pipe 55 and anexhaust pipe 56 are provided to thereby form a gas flow therein and toexhaust heat (see FIGS. 13 and 16). Air is supplied also to a gapbetween the chamber window 61 and the lamp light radiating window 53, tothereby cool the lamp house 5 and the chamber window 61.

Now, a procedure for processing a semiconductor wafer W will bediscussed. FIG. 18 is a flowchart showing part of an operation flow forprocessing the semiconductor wafer W in accordance with the secondpreferred embodiment. First, patterns are formed on a surface of thesilicon substrate 11 (see FIG. 20) by using a photolithography techniqueand impurities (ions) such as boron (B) or arsenic (As) are implantedinto a source/drain region (Step S101). The impurity implantation isperformed by ion implantation.

Subsequently, a carbon (C) thin film 12 is formed on the surface of thesilicon substrate 11 implanted with the impurities (Step S102). Forformation of the carbon thin film 12, various well-known techniques maybe adopted. For example, the carbon thin film 12 may be formed bydepositing carbon through plasma deposition. FIG. 20 is a cross sectionof a semiconductor wafer W immediately after the carbon thin film 12 isformed on the surface of the silicon substrate 11. In the secondpreferred embodiment, on the surface of the silicon substrate 11implanted with the impurities by ion implantation, the amorphous carbonthin film 12 is deposited and formed by plasma deposition. The filmthickness of the thin film 12 immediately after being deposited byplasma deposition is generally uniform in the plane of the siliconsubstrate 11, and in the second preferred embodiment, the film thickness(the initial value of the film thickness) of the amorphous carbon thinfilm 12 deposited on the surface of the silicon substrate 11 is 100 nmor more. As shown in FIG. 20, the carbon thin film 12 is formed,slightly getting round to the side end portion of the silicon substrate11.

Next, after the semiconductor wafer W with the carbon thin film 12deposited thereon is loaded into the heat treatment apparatus 1, thecarbon thin film 12 is processed (Step S103), and the light irradiationheat treatment is performed on the semiconductor wafer W (Step S104).The carbon thin film processing and the light irradiation heat treatmentwill be discussed later in more detail.

After the light irradiation heat treatment is finished by the heattreatment apparatus 1, cleaning of the semiconductor wafer W isperformed (Step S105). This cleaning process includes so-called SPMcleaning (using a mixture of sulfuric acid and oxygenated water) and APMcleaning (using a mixture of aqueous ammonia and oxygenated water). Byperforming this cleaning process, the carbon thin film 12 is completelyremoved from the surface of the silicon substrate 11.

FIG. 19 is a flowchart showing process steps for processing thesemiconductor wafer W in the heat treatment apparatus 1 in accordancewith the second preferred embodiment. In the second preferredembodiment, the heat treatment apparatus 1 performs both the processingof the carbon thin film 12 and the subsequent light irradiation heattreatment. The procedure of FIG. 19 for processing the semiconductorwafer W is carried out by the controller 3 controlling the operationmechanisms of the heat treatment apparatus 1.

First, the holder 7 moves down from the processing position shown inFIG. 16 to the transfer position shown in FIG. 13 (Step S111). The“processing position” is a position where the holder 7 is located whenthe semiconductor wafer W is irradiated with light from the flash lampsFL, which is the position of the holder 7 in the chamber 6 shown in FIG.16. The “transfer position” is a position where the holder 7 is locatedwhen the semiconductor wafer W is loaded or unloaded into/from thechamber 6, which is the position of the holder 7 in the chamber 6 shownin FIG. 13. The reference position of the holder 7 in the heat treatmentapparatus 1 is the processing position. Before the processing, theholder 7 is located at the processing position, and when the processingstarts, the holder 7 moves down to the transfer position.

The holder 7 moves up and down relative to the support pins 70 fixed tothe chamber 6. As shown in FIG. 13, moving down to the transferposition, the holder 7 comes close to the chamber bottom portion 62 andthe respective tips of the support pins 70 penetrate the holder 7 andprotrude over the holder 7.

Next, after the holder 7 moves down to the transfer position, the gasvalve 82 is opened and an inert gas (nitrogen gas in this preferredembodiment) is thereby supplied into the heat treatment space 65 of thechamber 6 from the gas source 88. At the same time, the gas valves 87and 473 are opened and the gas is thereby exhausted from the heattreatment space 65 (Step S112). The nitrogen gas supplied from the gasoutlet 89 into the chamber 6 flows downwardly toward the bottom opening64 located at the center of the chamber bottom portion 62 in the heattreatment space 65 and is exhausted through the gas exhaust outlet 472to the outside of the chamber 6. Part of the nitrogen gas supplied intothe chamber 6 is exhausted also from the outlet passage 86

Subsequently, the gate valve 185 is opened to open the transport opening66, and the semiconductor wafer W with the carbon thin film 12 formed onits surface is loaded into the chamber 6 through the transport opening66 by a transfer robot provided outside this apparatus and placed on theplurality of support pins 70 (Step S113). After the semiconductor waferW is loaded into the chamber 6, the transport opening 66 is closed bythe gate valve 185. Then, the holder elevating mechanism 4 moves theholder 7 from the transfer position up to the processing position nearthe chamber window 61 (Step S114). In the course of moving the holder 7up from the transfer position, the semiconductor wafer W is passed fromthe support pins 70 to the susceptor 72 of the holder 7 and placed onthe upper surface of the susceptor 72 to be held thereon. When theholder 7 moves up to the processing position, the semiconductor wafer Wheld by the susceptor 72 is also held at the processing position. Thesemiconductor wafer W held at the processing position is located alittle above the gas outlet 89.

Each of the six zones 711 to 716 of the hot plate 71 is already heatedup to a predetermined temperature by the heater (the resistance heatingwires 76) which is individually provided within the zone (between theupper plate 73 and the lower plate 74). The holder 7 is moved up to theprocessing position and the semiconductor wafer W comes into contactwith the holder 7, whereby the semiconductor wafer W is preheated by theheaters incorporated in the hot plate 71 and the temperature thereofincreases gradually (Step S115).

The preheating of the semiconductor wafer W increases the temperature ofthe semiconductor wafer W up to a preheating temperature T1 which is setin advance. The preheating temperature T1 is set ranging from about 200°C. to about 600° C., preferably from about 350° C. to about 550° C.(500° C. in the second preferred embodiment), at which there is noapprehension that the impurities implanted in the semiconductor wafer Wmight be diffused by heat. The distance between the holder 7 and thechamber window 61 is arbitrarily adjustable by controlling the amount ofrotation of the motor 40 of the holder elevating mechanism 4.

Concurrently with the preheating of the semiconductor wafer W performedat the processing position, oxygen gas is introduced into the heattreatment space 65 of the chamber 6 (Step S116). Specifically, theoxygen gas is supplied into the heat treatment space 65 from the gassource 88 through the gas inlet passage 81. At that time, only theoxygen gas may be supplied or a mixed gas of nitrogen gas and oxygen gasmay be supplied. The flow rate of the oxygen gas to be supplied into theheat treatment space 65 from the gas source 88 is controlled by thecontroller 3 controlling the flow rate regulating valve 85.

While the oxygen gas is supplied into the heat treatment space 65, theatmosphere is continuously exhausted from the chamber 6 (Step S117).Specifically, the gas valve 473 is opened to exhaust the gas from theheat treatment space 65 through the gas exhaust outlet 472. The flowrate of the gas to be exhausted through the gas exhaust outlet 472 iscontrolled by the controller 3 controlling the flow rate regulatingvalve 475. Part of the atmosphere in the chamber 6 is exhausted alsothrough the outlet passage 86. The flow rate of the gas to be exhaustedthrough the gas exhaust outlet 472 is significantly larger than the flowrate of the gas to be exhausted through the outlet passage 86.

FIG. 21 is a schematic view showing an airflow formed in the chamber 6.The gas outlet 89 is a ring-shaped slit formed on the chamber sideportion 63 a little below the holder 7 located at the processingposition (exactly, between the chamber side portion 63 and the ring 631)along the horizontal direction. Accordingly, the gas outlet 89 is soformed in a slit shape as to surround the semiconductor wafer W held bythe holder 7 at the processing position, which allows uniform supply ofgas containing the oxygen gas from around the semiconductor wafer W. Onthe other hand, the atmosphere in the chamber 6 is exhausted from thegas exhaust outlet 472 through the center of the chamber bottom portion62, i.e., the bottom opening 64 located immediately below near thecenter of the holder 7. Therefore, the atmosphere in the chamber 6 isexhausted from below the semiconductor wafer W held by the holder 7located at the processing position.

The above-discussed supply/exhaustion of gas causes such an airflowcontaining oxygen gas as shown in FIG. 21 inside the chamber 6. Most ofthe airflow containing the oxygen gas discharged from the slit-like gasoutlet 89 flows from the underside of the holder 7 located at theprocessing position toward the bottom opening 64, but some of theairflow also flows to the upper side of the holder 7 (the front surfaceside of the semiconductor wafer W). Since there is a negative pressurearound the bottom opening 64 inside the chamber 6, the airflow flowingto the upper side of the holder 7 also passes by the side of the holder7 and flows toward the bottom opening 64 in the end. Consequently, theairflow containing the oxygen gas continues to be supplied to theperipheral portion of the semiconductor wafer W to some degree buthardly reaches near the central portion. In other words, more oxygen gasis supplied to the peripheral portion of the semiconductor wafer W heldby the holder 7 located at the processing position than to the centralportion thereof.

When the oxygen gas is supplied to the surface of the semiconductorwafer W of which the temperature is raised to a preheating temperatureT1, the carbon of the thin film 12 reacts with oxygen to produce carbondioxide (CO₂) or carbon monoxide (CO). The carbon of the thin film 12 isthus vaporized, being consumed, and the film thickness of the thin film12 decreases. In other words, the carbon thin film 12 is etched bysupplying the oxygen gas to the preheated semiconductor wafer W. Sincethe produced oxide of carbon is gas, the gas is exhausted together withthe atmosphere in the chamber 6 through the gas exhaust outlet 472 andthe outlet passage 86 to the outside of the heat treatment apparatus 1.

At that time, since more oxygen gas is supplied to the peripheralportion of the semiconductor wafer W than to the central portionthereof, the consumption rate of carbon (i.e., the etching rate of thethin film 12) gradually becomes larger in the peripheral portion than inthe central portion. As a result, performed is a processing by which theamorphous carbon thin film 12 deposited on the surface of the siliconsubstrate 11 gradually becomes thinner from its central portion towardits peripheral portion continuously (in an analog manner). This is acarbon thin film processing in Step S103 of FIG. 18.

There needs a standby for a predetermined time in the state where theoxygen gas is supplied to the preheated semiconductor wafer W held bythe holder 7 located at the processing position as discussed above (StepS118). The standby time depends on the preheating temperature T1 and hasto become longer as the preheating temperature T1 becomes lower. In thesecond preferred embodiment, the preheating temperature T1 is 500° C.and in this case, the standby time is two to three minutes. This allowsa processing by which the carbon thin film 12 gradually becomes thinnercontinuously from its central portion toward its peripheral portion toproceed, and the difference in the film thickness between the centralportion of the thin film 12 and the peripheral portion thereof becomes apredetermined value or more.

FIG. 22 is a cross section of the semiconductor wafer W after the carbonthin film 12 is processed. By supplying more oxygen gas to the surfaceof the preheated semiconductor wafer W in its peripheral portion than toits central portion, the processing by which the thin film 12 becomesthinner from its central portion toward its peripheral portion isperformed and on the surface of the silicon substrate 11, formed is thethin film 12 (like a convex lens) which gradually becomes thinnercontinuously from its central portion toward its peripheral portion. Atthe point of time after a predetermined standby time has elapsed in StepS118, the processing is performed so that the difference td between thefilm thickness tc of the central portion of the carbon thin film 12 andthe film thickness te of the peripheral portion thereof may be not lessthan 8 nm and not more than 30 nm. In the second preferred embodiment,the film thickness tc of the central portion of the thin film 12 isabout 80 nm and the film thickness te of the peripheral portion thereofis about 70 nm.

At the point of time after a predetermined standby time has elapsed inStep S118, the flash light is emitted from the flash lamps FL of thelamp house 5 toward the semiconductor wafer W under the control of thecontroller 3 in the state where the holder 7 is located at theprocessing position (Step S119). At that time, part of the flash lightemitted from the flash lamps FL travels directly to the holder 7 insidethe chamber 6. The remainder of the flash light is reflected by thereflector 52, and the reflected light travels to the inside of thechamber 6. With such emission of the flash light, the flash heating isperformed on the semiconductor wafer W. The flash heating, which isachieved by emission of the flash light from the flash lamps FL, canraise the surface temperature of the semiconductor wafer W in a shorttime.

Specifically, the flash light emitted from the flash lamps FL of thelamp house 5 is an extremely short and intense flash of light emittedfor a period of time not shorter than 0.1 milliseconds and not longerthan 100 milliseconds because the previously stored electrostatic energyis converted into such an ultrashort light pulse. The surfacetemperature of the semiconductor wafer W (exactly, the surfacetemperature of the carbon thin film 12) subjected to the flash heatingby emission of flash light from the flash lamps FL instantaneously risesto a treatment temperature T2, and after the impurities implanted in thesemiconductor wafer W are activated, the surface temperature fallsquickly. In the heat treatment apparatus 1, since the surfacetemperature of the semiconductor wafer W can be increased and decreasedin an extremely short time, activation of the impurities implanted inthe semiconductor wafer W can be achieved while the diffusion of theimpurities due to heat is suppressed. Since the time period required forthe activation of the impurities is extremely short as compared with thetime period required for the thermal diffusion of the impurities, theactivation is completed even in a short time ranging from about 0.1 toabout 100 milliseconds during which no diffusion occurs. This is a lightirradiation heat treatment in Step S104 of FIG. 18.

On the surface of the semiconductor wafer W to be treated, the carbonthin film 12 is formed. As the film thickness of the carbon thin film 12becomes larger, the surface reflectance of the semiconductor wafer Wdecreases, and when the film thickness is 70 nm, the surface reflectanceis about 60%. The decrease in the surface reflectance means the increasein the absorptivity of flash light in the semiconductor wafer W, andmore specifically, it means the increase in the absorptivity of flashlight in the carbon thin film 12. The spectral distribution of radiationof flash light from the xenon flash lamps FL ranges from ultraviolet tonear-infrared regions and the flash light hardly passes through thesilicon substrate 11.

The decrease in the surface reflectance of the semiconductor wafer Wwith the increase in the film thickness of the carbon thin film 12 iscaused by the increase in the absorptivity of flash light in the carbonthin film 12 with the increase in the film thickness thereof.Specifically, when the carbon thin film 12 becomes thick to some degreeor more, part of the emitted flash light is absorbed by the thin film12. The absorptivity becomes larger as the film thickness of the thinfilm 12 becomes larger. Heat is generated on the surface of the carbonthin film 12 which has absorbed the flash light and the heat istransferred to the surface of the silicon substrate 11.

Thus, the carbon thin film 12 having a given film thickness or morefunctions as a light absorption film to increase the absorptivity offlash light in the semiconductor wafer W. As a result of increasing theabsorptivity of flash light in the semiconductor wafer W, the attainedsurface temperature of the semiconductor wafer W during the irradiationwith flash light (strictly describing, the attained surface temperatureof the surface of the silicon substrate 11 implanted with theimpurities) increases as compared with that in the case where no thinfilm is formed, and this allows better activation of the impurities tobe achieved.

Especially, in the second preferred embodiment, the thin film 12 isformed so that its film thickness may gradually become smallercontinuously from its central portion toward its peripheral portion. Theabsorptivity of flash light accordingly becomes higher in the centralportion of the semiconductor wafer W than in the peripheral portionthereof. On the other hand, as discussed above, the intensitydistribution of the flash light in the plane of the semiconductor waferW during the irradiation with flash light is not completely uniform, andthere is a tendency that the light intensity becomes higher in theperipheral portion of the semiconductor wafer W than in the centralportion thereof due to the effect of reflection on the chamber sideportion 63 and the like. In other words, in the peripheral portion ofthe semiconductor wafer W where the light intensity becomes higherduring the irradiation with flash light, the absorptivity of flash lightis lower, and in the central portion of the semiconductor wafer W wherethe light intensity becomes lower, to absorptivity of flash light ishigh. As a result, the degree of increase in the temperature of the thinfilm 12 serving as the light absorption film is generally uniform in theplane of the semiconductor wafer W, and the inplane temperaturedistribution of the semiconductor wafer W during the irradiation withflash light can be made uniform. Thus, by forming the thin film 12 sothat its film thickness gradually becomes smaller continuously from thecentral portion of the semiconductor wafer W toward the peripheralportion thereof, it is possible to raise the surface temperature of thesemiconductor wafer W uniformly to be still higher and achieve betteractivation of the impurities, and the sheet resistance value can be alsouniformly decreased.

The reason why the difference td between the film thickness tc of thecentral portion of the thin film 12 and the film thickness to of theperipheral portion thereof is set to not less than 8 nm and not morethan 30 nm is as follows. If the difference td in the film thickness isless than 8 nm, such an effect of achieving higher absorptivity of flashlight in the central portion than in the peripheral portion as discussedabove is hardly produced, and the temperature of the peripheral portionof the semiconductor wafer W which is irradiated with the flash light ofhigher intensity becomes higher than that of the central portionthereof. On the other hand, if the difference td in the film thicknessis more than 30 nm, the absorptivity of flash light in the centralportion becomes too high as compared with that in the peripheralportion, and the temperature of the central portion of the semiconductorwafer W during the irradiation with flash light becomes higher than thatof the peripheral portion thereof. In other words, if the difference tdin the film thickness between the central portion of the thin film 12and the peripheral portion thereof is out of the range not less than 8nm and not more than 30 nm, it becomes difficult to uniformize theinplane temperature distribution of the semiconductor wafer W during theirradiation with flash light.

The flash light emitted from the flash lamps FL is once absorbed by thecarbon thin film 12 and this causes heat in the thin film 12, and thenthe heat is transferred to the surface of the silicon substrate 11.Therefore, even if there is variation of the absorptivity in the surfaceof the silicon substrate 11 due to formation of patterns, the variationof the absorptivity can be eased as compared with the case where no thinfilm is formed, and the surface of the silicon substrate 11 implantedwith the impurities is thereby uniformly heated.

Also when the flash light is emitted from the flash lamps FL, the oxygengas is supplied into the chamber 6 from the gas outlet 89 while theatmosphere continues to be exhausted from the chamber 6 through the gasexhaust outlet 472. Therefore, the carbon of the thin film 12 heated byirradiation with flash light reacts with oxygen to produce carbondioxide (CO₂) or carbon monoxide (CO). The carbon of the thin film 12 isthus vaporized, being consumed, and the film thickness of the thin film12 decreases. In other words, the carbon thin film 12 is removed byintroduction of oxygen into the chamber 6 while serving as a lightabsorption film during the irradiation with flash light. Since theproduced oxide of carbon is gas, the gas is exhausted together with theatmosphere in the chamber 6 through the gas exhaust outlet 472 and theoutlet passage 86 to the outside of the heat treatment apparatus 1.

After the lapse of predetermined time (several seconds) from the end ofthe flash heating, nitrogen gas is supplied again into the heattreatment space 65 from the gas source 88 while the gas containing theoxygen gas is exhausted from the heat treatment space 65 through the gasexhaust outlet 472 and the outlet passage 86. The atmosphere in thechamber 6 is thereby substituted with the nitrogen gas (Step S120).

Then, the holder 7 is moved down again to the transfer position shown inFIG. 13 by the holder elevating mechanism 4, and the semiconductor waferW is passed from the holder 7 to the support pins 70 (Step S121).Subsequently, the gate valve 185 opens the transport opening 66 havingbeen closed, and the transfer robot provided outside this apparatusunloads the semiconductor wafer W rested on the support pins 70. Thus,the flash heat treatment (annealing process) on the semiconductor waferW in the heat treatment apparatus 1 is completed (Step S122).

As discussed above, in the second preferred embodiment, formation of thecarbon thin film 12 on the surface of the semiconductor wafer W allowsthe carbon thin film 12 to absorb the flash light. Absorbing the flashlight causes the temperature of the carbon thin film 12 to rise, and itis thereby possible to increase the surface temperature of the siliconsubstrate 11 implanted with the impurities to be still higher anddecrease the sheet resistance value as compared with the case where nothin film is formed.

Particularly, in the second preferred embodiment, by supplying moreoxygen gas to the peripheral portion of the semiconductor wafer W thanto the central portion thereof while preheating the semiconductor waferW, the processing by which the carbon thin film 12 becomes thinner fromits central portion toward its peripheral portion is performed.Therefore, on the surface of the semiconductor wafer W, formed is thethin film 12 which gradually becomes thinner continuously from itscentral portion where the intensity of flash light is lower toward itsperipheral portion where the intensity of flash light is higher. Thiscompensates for the variation in the intensity distribution of the flashlight and uniformizes the inplane temperature distribution of thesemiconductor wafer W during the irradiation with the flash light.Further, the surface temperature of the semiconductor wafer W can beuniformly increased to be still higher and the sheet resistance valuecan be decreased. By uniformizing the inplane temperature distributionof the semiconductor wafer W during the irradiation with the flashlight, it is possible to suppress a break in the semiconductor wafer W.Since the thin film 12 gradually becomes thinner, the absorptivity oflight in the plane of the semiconductor wafer W does not sharply changeand this makes the inplane temperature distribution of the semiconductorwafer W more uniform.

Since the semiconductor wafer W with carbon thin film 12 formed thereonis irradiated with the flash light while the oxygen gas is supplied intothe chamber 6, the carbon of the heated thin film 12 is oxidized andthus vaporized, thereby being consumed. This allows the removal of thecarbon thin film 12 to proceed during the flash heating, and theremaining film of carbon can be removed only by the normal SPM cleaningand APM cleaning in the subsequent cleaning process (Step S105 of FIG.18). If the flash light is emitted in the atmosphere of inert gas suchas nitrogen gas inside the chamber 6, since the carbon of the thin film12 is not consumed, the original film thickness is generally maintainedeven after the flash heating. In this case, the thin film 12 is notfully removed only by the normal SPM cleaning and APM cleaning and theashing process is additionally needed before the cleaning process ofStep S105. As shown in the second preferred embodiment, if theirradiation with the flash light is performed while the oxygen gas issupplied into the chamber 6, the removal of the thin film 12 can beperformed concurrently with the flash heating, and therefore, no ashingprocess is needed and the remaining film can be reliably removed only bythe normal cleaning process. The carbon thin film 12 is not entirelyvaporized during the emission of flash light, and the remaining filmalso serves as an antioxidizing film for the surface of the siliconsubstrate 11.

<Variations>

Though the preferred embodiments of the present invention have beendiscussed above, the present invention allows various variations otherthan the above-discussed embodiments without departing from the scope ofthe invention. For example, though the amorphous carbon thin film 12 isformed on the surface of the silicon substrate 11 implanted withimpurities in the above preferred embodiments, a thin film of carbonhaving a crystal structure (e.g., graphite), instead of amorphouscarbon, may be formed. Even if the thin film 12 of carbon having acrystal structure is formed, the same effect as discussed in the abovepreferred embodiments can be produced. When the thin film 12 is made ofamorphous carbon, however, the thin film 12 is easily oxidized duringthe flash heating and the removal of the thin film 12 can easilyproceed.

The thin film 12 may be formed of a carbon compound. One of carboncompounds suitable for the thin film 12 serving as a light absorptionfilm is especially an organic compound, and a favorable one is acompound containing carbon and hydrogen, or containing carbon, hydrogen,and oxygen. In other words, the thin film 12 has only to be formed ofcarbon or a carbon compound on the surface of the silicon substrate 11implanted with impurities.

Though the film thickness t of the amorphous carbon thin film 12 formedon the surface of the silicon substrate 11 is 70 nm in the firstpreferred embodiment, the film thickness t is not limited to this, butonly if the carbon or carbon compound thin film 12 having a filmthickness t of at least 20 nm or more is formed, the thin film 12 canproduce the effect as a light absorption film. Since the absorptivity offlash light in the thin film 12 increases as the film thickness of thethin film 12 becomes larger, however, in order to absorb more flashlight and raise the surface temperature of the silicon substrate 11 moreeffectively, it is desirable that the film thickness t of the thin film12 should be 70 nm or more. On the other hand, if the film thickness tof the thin film 12 becomes larger to exceed 280 nm, the thin film 12produces no significant change in the effect of raising the temperatureas a light absorption film and there arises a possibility instead thatthe thickness of the remaining film after the flash heating becomeslarger and the film cannot fully removed only by the subsequent cleaningprocess. Therefore, the favorable film thickness t of the carbon orcarbon compound thin film 12 formed on the surface of the siliconsubstrate 11 is not less than 70 nm and not more than 280 nm.

Though the oxygen concentration in the chamber 6 during the irradiationwith flash light is set to 90% or more in the first preferredembodiment, the oxygen concentration is not limited to this, but only ifeven a few amount of oxygen gas is present around the semiconductorwafer W during the irradiation with flash light, the effect of oxidizingthe carbon of the thin film 12 and removing the thin film 12 can beproduced. In order to produce both the effect of fully removing the thinfilm 12 and the effect of cancelling the nonuniformity in the inplanetemperature distribution due to the variation in the intensitydistribution of the flash light, however, it is desirable that theoxygen concentration in the chamber 6 during the irradiation with flashlight should be higher, and it is particularly preferable that theoxygen concentration should be set to 90% or more. If the oxygenconcentration in the chamber 6 is 90% or more, it is possible to preventthe deposition of carbon-based contaminants on the inside of the chamber6 during the irradiation with flash light.

On the other hand, in terms of obtaining a lower sheet resistance value,it is desirable that the oxygen concentration in the chamber 6 duringthe irradiation with flash light should be lower. In order to produceall the effects of effectively removing the thin film 12, of preventingthe deposition of contaminants on the inside of the chamber 6, and ofcancelling the nonuniformity in the inplane temperature distribution,however, it is desirable that the oxygen concentration in the chamber 6during the irradiation with flash light should be higher than the oxygenconcentration in the atmosphere, and specifically the oxygenconcentration should be not lower than 21%. Therefore, the oxygenconcentration in the chamber 6 during the irradiation with flash lightmay be any value not lower than 21% and not higher than 100% inconsideration of the required sheet resistance value, the uniformity inthe inplane temperature distribution, the effect of removing the thinfilm 12, and the like. In order only to achieve a lower sheet resistancevalue, however, there may be a case where the semiconductor wafer W withthe carbon thin film 12 formed on its surface is irradiated with flashlight without introducing oxygen gas into the chamber 6 (for example,with nitrogen atmosphere inside the chamber 6).

In the first preferred embodiment, the timing at which the oxygen gas isintroduced into the chamber 6 is not limited to the exemplary one shownin FIG. 8 but the oxygen gas may be introduced before the preheating. Inother words, only if the oxygen concentration in the chamber 6 duringthe irradiation with flash light takes a predetermined value, the oxygengas may be introduced into the chamber 6 at any timing.

Though the film thickness of the thin film 12 becomes smaller from itscentral portion toward its peripheral portion in the second preferredembodiment, the film thickness distribution is not limited to this butthe distribution of the film thickness of the thin film 12 has only tobe such one as to compensate for the variation in the intensitydistribution of the flash light. If there is an intensity distributionin which the light intensity becomes higher in the central portion ofthe semiconductor wafer W than in the peripheral portion thereof,contrary to the second preferred embodiment, the film thickness of thethin film 12 has only to become smaller from its peripheral portiontoward its central portion (like a concave lens). In other words, such athin film has only to be formed as to compensate for the variation inthe intensity distribution of the flash light in the plane of thesemiconductor wafer W during the irradiation with the flash light, andmore specifically, as to have a nonuniform film thickness distributionin which the film thickness becomes smaller at the positions where theintensity of flash light is higher.

Though the processing by which the carbon thin film 12 becomes thinnerfrom its central portion toward its peripheral portion is performed bysupplying more oxygen gas to the peripheral portion of the semiconductorwafer W than to the central portion thereof while preheating thesemiconductor wafer W in the second preferred embodiment, the processingof the carbon thin film 12 is not limited to this. There may be a case,for example, where a plurality of flash lamps having different diametersare arranged concentrically in the lamp house 5 and while oxygen gas issupplied to the surface of the semiconductor wafer W, only theperipheral portion of the semiconductor wafer W is irradiated with lessintense flash light, whereby a difference in the film thickness isproduced. In this case, after the irradiation with the less intenseflash light for processing the carbon thin film 12, the irradiation withflash light is performed, like in Step S119 of FIG. 19, to activate theimpurities. Since the hot plate 71 of the holder 7 for preheating thesemiconductor wafer W is divided into a plurality of zones arrangedconcentrically (see FIG. 4), there may be another case where whileoxygen gas is supplied to the surface of the semiconductor wafer W,preheating is performed so that the temperature of the peripheralportion of the semiconductor wafer W becomes higher than that of thecentral portion thereof, to thereby produce a difference in the filmthickness. Specifically, in the preheating, the controller 3 controlsthe plate power supply 98 so that the temperature of the zone 712 maybecome higher than that of the zone 711 and the respective temperaturesof the zones 713 to 716 may become higher than that of the zone 712.

In the second preferred embodiment, there may be still another casewhere the carbon thin film processing is additionally performed beforethe semiconductor wafer W with the carbon thin film 12 deposited thereon(the wafer shown in FIG. 20) is loaded into the heat treatment apparatus1. For example, the semiconductor wafer W with the carbon thin film 12deposited thereon is loaded into an apparatus for performing beveletching and only the peripheral portion of the semiconductor wafer W isetched with hydrofluoric acid or the like. Alternatively, in the processstep of performing plasma deposition on the surface of the siliconsubstrate 11, a thin film 12 may be deposited so that its film thicknessgradually becomes smaller from the central portion of the semiconductorwafer W toward the peripheral portion thereof.

In the second preferred embodiment, the material for the thin film 12 tobe formed on the surface of the silicon substrate 11 is not limited tocarbon but any material having the physical properties of absorbingflash light may be used. For example, the thin film 12 may be formed ofsilicon nitride (SiN)) or may be formed of a metal-based reflectionfilm/absorption film. As the metal-based reflection film,polysilicon+germanium (Ge), polysilicon+arsenic (As), MgF₂, CaF₂, SiGe,Ge, GaAs, InSb, Cr, Mo, Nb, Zr, Y, Ti, a compound of La and oxygen (O),nitrogen (N), or carbon (C), or AlN may be used. As the metal-basedabsorption film, SiO₂, SiON, or Si₃N₄ in which crystallized carbon (C)contains hydrogen (H) or oxygen (O) may be used. Even if the thin film12 is formed of any one of these materials, when the thin film 12 isformed so that its film thickness may gradually become smaller from thecentral portion of the semiconductor wafer W toward the peripheralportion thereof, the absorptivity of flash light becomes higher in thecentral portion of the semiconductor wafer W than in the peripheralportion thereof. As a result, like in the second preferred embodiment,the inplane temperature distribution of the semiconductor wafer W duringthe irradiation with flash light can be made uniform. If the thin film12 is formed of silicon nitride or the metal-based reflection film,however, since the processing of the thin film 12 cannot be performed byheating and supply of oxygen gas, it is necessary to perform theprocessing for producing a difference in the film thickness by beveletching with hydrofluoric acid or the like before the wafer is loadedinto the heat treatment apparatus 1.

In the second preferred embodiment, a plural-layered thin film may beformed on the surface of the silicon substrate 11. FIG. 23 is a crosssection of a semiconductor wafer W in which a double-layered thin filmis formed on the surface of the silicon substrate 11. On the surface ofthe silicon substrate 11 implanted with the impurities by ionimplantation, a carbon or carbon compound thin film 12 a (first thinfilm) is deposited and formed, like in the second preferred embodiment,and further, a polysilicon thin film 12 b (second thin film) of whichthe film thickness becomes smaller from its central portion toward itsperipheral portion is formed. The film thickness processing ofpolysilicon can be performed by bevel etching with hydrofluoric acid orthe like. This also makes the absorptivity of flash light in the centralportion of the semiconductor wafer W higher than that in the peripheralportion thereof and uniformize the inplane temperature distribution ofthe semiconductor wafer W during the irradiation with flash light.Further, during the irradiation with flash light, scattering ofcarbon-based contaminants from the lower thin film 12 a can besuppressed with the upper thin film 12 b and this prevents deposition ofsuch contaminants on the structure inside the chamber 6. In FIG. 23,even if the thin film 12 b is formed of amorphous silicon or siliconnitride, the same effect can be produced.

Though the lamp house 5 is provided with thirty flash lamps FL in theabove preferred embodiments, the number of flash lamps FL is not limitedto this but an arbitrary number of flash lamps FL may be provided. Theflash lamp FL is not limited to a xenon flash lamp but may be a kryptonflash lamp.

Though the semiconductor wafer W is preheated by heat transferred fromthe holder 7 including the hot plate 71 in the above preferredembodiments, there may be a case where halogen lamps are provided at thebottom of the chamber 6 and the semiconductor wafer W is preheated byirradiation with light emitted from the halogen lamps. In the secondpreferred embodiment, even if the processing by which the carbon thinfilm 12 becomes thinner from its central portion toward its peripheralportion is performed by supplying more oxygen gas to the peripheralportion of the semiconductor wafer W than to the central portion thereofwhile preheating the semiconductor wafer W by irradiation with the lightemitted from the halogen lamps, the same effect as discussed above canbe produced.

The techniques in accordance with the present invention can be alsoapplied to a glass substrate on which a silicon film is formed.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A heat treatment apparatus for heating asubstrate implanted with impurities by irradiating the substrate withflash light, comprising: a chamber for housing a substrate in which acarbon or carbon compound thin film is formed on a surface thereof afterbeing implanted with impurities; a holding part for holding saidsubstrate in said chamber; a flash lamp for emitting flash light to saidsubstrate held by said holding part, further comprising an oxygenintroduction part for introducing oxygen gas into said chamber; and acontrol part configured to house said substrate in said chamber, andthereafter introduce oxygen gas from said oxygen introduction part intosaid chamber before emitting the flash light, and then control saidflash lamp to emit flash light to said substrate in the oxygenatmosphere.
 2. The heat treatment apparatus according to claim 1,wherein said oxygen introduction part sets the oxygen concentration to90% or more in said chamber at the point of time when flash light isemitted from said flash lamp.
 3. The heat treatment apparatus accordingto claim 2, further comprising a control part for controlling saidoxygen introduction part to set the oxygen concentration to 90% or morein said chamber and controlling said flash lamp to emit flash light tothe inside of said chamber in which the oxygen concentration is set to90% or more when no substrate is housed in said chamber.
 4. The heattreatment apparatus according to claim 1, wherein the thickness of saidthin film is not less than 70 nm and not more than 280 nm.
 5. The heattreatment apparatus according to claim 1, wherein the material of saidthin film is amorphous carbon.
 6. A heat treatment apparatus for heatinga substrate implanted with impurities by irradiating the substrate withflash light, comprising: a chamber for housing a substrate in which acarbon or carbon compound thin film is formed on a surface thereof afterbeing implanted with impurities; a holding part for holding saidsubstrate in said chamber; a preheating part for preheating saidsubstrate held by said holding part; a flash lamp for emitting flashlight to said substrate held by said holding part; an oxygen gas supplypart for supplying oxygen gas from around said substrate held by saidholding part in said chamber; an exhaust part for exhausting theatmosphere in said chamber from below said substrate held by saidholding part; and a control part configured to control said preheatingpart to heat said substrate held by said holding part, control saidoxygen gas supply part to supply oxygen gas while controlling saidexhaust part to exhaust the atmosphere from said chamber, to therebymake the film thickness smaller from the central portion of said thinfilm formed on said surface of said substrate toward the peripheralportion thereof, and then control said flash lamp to emit flash light.7. The heat treatment apparatus according to claim 6, wherein thedifference in the film thickness between the central portion of saidthin film and the peripheral portion thereof is not less than 8 nm andnot more than 30 nm when flash light is emitted.